Apparatus for carrying out cranium radiographs and teleradiographs according to a plurality of projections

ABSTRACT

An apparatus is disclosed for carrying out cranium and dental arches radiographs and teleradiographs according to a plurality of projections, comprising a vertical standard and a cross rod, at one end carrying a X-ray tube unit and at the other end a craniostat slidable along the rod and rotating according to a horizontal axis, which craniostat can be blocked at any desired adjusted position. Said cross rod is pivoted, according to a horizontal axis at right angles to said standard, to a sliding block or shoe slidable and blockable at any desired position along said standard.

United States Patent [191 Poggio APPARATUS FOR CARRYING OUT CRANIUM RADIOGRAPHS AND TELERADIOGRAPHS ACCORDING TO A PLURALITY OF PROJECTIONS [76] Inventor: Francesco Poggio, Piazza Velasca 4,

Milan, Italy [22] Filed: Aug. 14, 1972 [21] Appl. No.: 280,216

[30] Foreign Application Priority Data Aug. 21, 1971 Italy 27711/71 [52] US. Cl. 250/448, 250/523 [51] Int. Cl. G03b 41/16 [58] Field of Search 250/61.5, 91, 70, 50

[56]. References Cited UNITED STATES PATENTS 2,264.410 12/1941 Schier 250/50 3,536,913 10/1970 Huchel 250/50 451 Apr. 30, 1974 3,524,057 8/1970 Hammonds 250/50 2,903,588 9/1959 Minnich 6/ 1972 Moss 250/615 ABSTRACT An apparatus is disclosed for carrying out cranium and dental arches radiographs and teleradiographs according to a plurality of projections, comprising a vertical standard and a cross rod, at one end carrying a X-ray tube unit and at the other end a craniostat slidable along the rod and rotating according to a horizontal axis, which craniostat can be blockedat any desired adjusted position. Said cross rod is pivoted, according to a horizontal axis at right angles to said standard, to a sliding block or shoe slidable and blockable at any desired position along said standard.

15 Claims, 16 Drawing Figures PATENTED R 30 m4 SHEEI 2 0F 4 I PATENTED APR 30 m4 saw u' or 4 APPARATUS FOR CARRYING OUT CRANIUM RADIOGRAPHS AND TELERADIOGRAPI-IS ACCORDING TO A PLURALITY OF PROJECTIONS In the medico-dental art it is required to carry out dental arches or cranium radiographs or teleradiographs in a plurality of projections. At present there are apparatuses wherein the stand, or supporting member for the X-ray tube and craniostat, comprises a vertical standard, a cross element being vertically slidable thereon and formed of two generally non aligned arms. At one end thereof this cross element carries the X-ray tube unit, and at the other end fixedly carries the craniostat unit for positioning a patients head and the radiographic plate. In such apparatuses the craniostat com prises a cap or dome-like element containing the earcap adjusting means. By these apparatuses of the prior art, it was possible to carry out side and front teleradio graphs, while top, bottom, right or lefi side occlusal ra diographs had to be carried out on additional apparatuses, thereby involving an increased cost and larger overall size.

It is the object of the present invention to obviate these disadvantages by providing an apparatus enabling one, by suitable ready movements of the cross supporting element or craniostat, to carry out side and front teleradiographs, top and bottom occlusal radiographs, and left and right side radiographs on such an apparatus.

Therefore, the present invention relates to an appara# tus for carrying our cranium and dental arches teleradiographs according to a plurality of projections, the ap paratus being adapted to take the most suitable position for each projection by height sliding of the cross element supporting the craniostat and X-ray tube and rotation of said element relative to the stationary standard. Moreover, this rotation can be completed so as to position the X=ray tube to the right or to the left of the standard in accordance with'the required adaptation. v

The present invention also relates to a craniostat for use on such an apparatus, as longitudinally movable along said cross arm and rotable about an axis at right angles thereto, this craniostat being crown-shaped andsage also at the top occlusal radiography position, and

being provided with an orientable device for a patients head positioning.-

Particularly, according to the invention, the vertical standard of the stand is provided with guides and a vertically sliding shoe engaged thereon; this vertical sliding is carried out, controlled and blocked at the desired position in a known manner. The cross element is pivoted to the shoe or sliding block is rotatable relative to a horizontal axis and can be blocked at suitable positions. The cross element, hereinafter referred to as a rod," comprises two semirods, one of which having at an end the X-ray tube unit, which will not be described in detail as being of a conventional design; the semirod op-' posite said end carries the cranios'tat and plate unit.

The craniostat according to the'invention comprises two parts, that is a carrier or stationary" ring part (wherein by the term stationary is to be meant opposite to the term,movable" related to the other ring and not in an absolute sense), and a movable" ring pan,

the position of which is adjustable relative to the carrier.

ring, said movable ring being rotable about the central axis for the two parts. The movable ring bears on the carrier ring by means to be described in the following, and bodily carries the two earcaps, or any other suitable means for head positioning, as well as the adjusting means for said positioning means. The carrier ring is held with a supporting bracket which is connected to the cross rod, so as to be slidable the'realong and to rotate relative thereto about a horizontal axis. This dual movement can be accomplished by any coupling essentially comprising a shoe or sliding block carrying a pin. The plate-holder frame, which should necessarily be perpendicular to the ray direction, can be restrained to the sliding shoe, or can be restrained to the craniostat carrier ring; however, it should always be provided with a hinge for rotating it to some positions. 1

The invention also provides a means for checking the alignment of the earcaps when, for example, the craniostat is at the side teleradiographic position; this means comprises a small tube of ray-opaque metal of a given diameter and incorporated in one of said two earcaps, and a small cylinder of the same metal, such as lead, having a smaller diameter and being incorporated in the other of said two earcaps, so that, upon alignment of the earcaps and by projection thereof on a plate, an image is provided showing two concentric circles.

The invention will now be described with reference to the accompanying drawings, showing bymere way of example some preferred embodiments thereof, and in which: I

FIG. 1 is a front view of the apparatus according to the invention, as shown at an operative position (side teleradiography with X-ray tube unit at the left of the figure), while another'operative position (top occlusal radiography) is shown by broken lines;

FIG. 2 is a plan view of the apparatus at the side (or front) teleradiography position, the X-ray tube unitbeing at the left of the figure;

FIG. 3 is a front view of the apparatusat bottom occlusal radiography position with aside teleradiography position shown by broken lines, but wherein the X-ray tube unit is at the right of the figure;

FIG. 4 is a perspective partly sectional view through a shoe or sliding block and pin unit, enabling the cross rod to slide and rotate on the vertical standard;

FIGS. 5 and 6 are cross-sections through twoforms of the shoe or sliding block and pin unit enabling the craniostat supporting bracket to slide and rotate on the cross rod; 1 v q FIG. 7 shows a first embodiment of the craniostat in across-sectional view according to line 7-7 of FIG. 8;

FIG. 8 is a sectional view according to line 8-8 of FIG. 7;

12-12 of FIG. 13, showing a fourth type of craniostat;

- FIG. 13 is a view taken along line 13-13 of Pro. 12;

FIG. 14 is a perspective view of a plate holder frame mounted on the stationary ring of the craniostat;

' FIG. 15 is a perspective view of a plate holder frame mounted on a sliding shoe; and

FIG. 16 is a view showing a device for controlling the earcaps alignment.

In some figures of the drawings, the arrows show the movability directions for the several members.

As shown in FIGS. 1, 2 and 3, the apparatus comprises a vertical standard 1 carrying in a per se known manner sliding guides for a shoe or sliding block 2. This sliding block or shoe 2 can be blocked at any position by knownmeans, such as an electromagnetic brake. The shoe or sliding block 2 has a pin 3 (also shown in FIG. .4), on which a cross rod 4 is rotably pivoted at an intermediate position and can be blocked at any suitable position by known means. In the exemplary embodiment shown in FIG. 4, at the most frequently recurring positions, engaging holes or notches 6 are provided on pin 3 for a blocking means 5. On said shoe or sliding block 2, provision can be made also for a disk (not shown) carrying the degree indication or other measuring means for-the angles of rotation.

In the figures of the drawings, numerals 7, 7 generally designate control boxes.

At one end the cross crod 4 carries the X-ray tube unit, generally designated at 9, which is of a conventional design and therefore not described herein. The opposite semirod has sliding guides 10, a second sliding block or'shoe 11 sliding thereon and having a pin 12 carrying the supporting bracket 13 of the craniostat 20 and allowing the rotation thereof. The coupling for the sliding guidesand shoe or sliding block can be carried out in any suitable manner, for example as shown in FIGS. and 6. Particularly, in FIG. 5 the sliding guides are shown as longitudinal tubes, and the sliding block or shoe 11 is provided with corresponding sleeves 10'. In FIG. 6, the sliding guide comprises a plate 10A carried by said semirod and engaging a shoe or sliding block 1 1 provided with rollers 11B. Longitudinal sliding clamping can be effected, for example, by electromagnetic brakes, or by spring pegs projecting from the shoe or sliding block and engaging the sliding guide cavity; the rotation clamping can be effected by a frictional blocking device. Along with this device, or independently thereof, a number of notches 14 are provided on the surface of the shoe or sliding block 1 1 facing the bracket 13, at the recurring positions for engaging a means 15, spring projecting from said bracket surface 13 facing the shoe or sliding block 11.

This bracket 13 can assume several forms and performs the function of bodily retaining the craniostat 20. Particularly in the embodiment of the apparatus shown in FIG. 1, sincethe semirod 4 carrying the X-ray tube unit 9 and semirod 4A carrying the craniostat 20 are on the same axis, and since the earcaps and X-ray tube should be on the same axis, the size of bracket 13 has to be such as to bring the c raniostat 20 to the required level.

As above mentioned, to allow for also carrying out a top occlusal radiography, where the rays strike a patients head from above, the invention provides a crown craniostat (FIGS. 7 and 8), essentially comprising a stationary' ring 21 bodily carried on the bracket and a movable ring 22, the latter carrying the rods 23' for the earcaps 23. In the space between said two rings and on the movable ring 22, means are provided for adjusting said earcaps by a movement to and away from each other). In a preferred embodiment (FIGS. 7, 8 and 9) the craniostat 20 according to the invention comprises a stationary ring 21 of L-shaped cross-section, which is located at the top and outside, and a movable ring 22, but of inverted L-shaped cross-section, which is located at the bottom and inside. At the peripheral inside facing portion said ring 21 has an annular rib 24, rollers 25 of a concave contour (three in number in the drawings) engaging thereon, held fast to said movable ring 22 and supporting the latter hanging from the stationary ring 21 so as to rotate relative thereto.

The earcap position is adjusted by two levers 26 and 26 pivoted at 27 and 27 respectively, which are controlled by a single screw 28 through a peg engaging slits at the ends of levers 26 and 26'. These levers at the opposite ends control pegs 29 slidable within sleeves and fast with said earcap rods 23'.

Preferably, said ring 22 is manually driven relative to ring 21.

On the movable ring 22 a peg 30 (FIG. 9) is provided and spring urged into cavities or holes on the ring 21 at the most frequently recurring positions of one ring with respect to the other. a

Other methods for joining said two rings 21 and 22 and for adjusting the movement of the earcaps symmetrically to and away from each other are provided in FIGS. 10-13. I

Referring to FIG. 10, said movable ring 22 is shown as resting by a substantially horizontal extension 22A thereof through balls 31 on a substantially horizontal extension 21A of ring 21'. The rotation clamping peg 30, as carried on said stationary ring 21, engages perforated plates 36-fast with the movable ring 22. Each of the earcap rods 23' are joined to an inner screw meshing with asleeve nut screw 33.

By rotating this nut screw 33, said screw 32 is advanced and retracted. Each of the nut screws 33 are held fast to a gear wheel 34 meshing with an internally toothed crown 35, the latter resting by balls 44 on an extension 22c held fast to ring 22. It will be readily evident that on rotating through a given angle the nut screw 33 controlling a rod 23, the nut screw contr'olling the other symmetric rod 23 will rotate to the same extent and the movements of the rods will also be symmetrical. 7

FIG. 11 shows a modified method relative to that of F IG. 10. In this embodiment the movable ring 22 is .car-' ried on the stationary ring 21 by rollers 25 of a concave contour, as in the case of FIG. 7. Similar rollers 37, also held fast to said movable ring 22, provide for carrying a crown 35' which is toothed at the top and meshed with a gear wheel 34 for each earcap, respectively; by j a nut screw 38 each of the gear wheels 34' control a respective earcap adjusting screw. In this case, the adjust: ment' is directly accomplished by rotating said crown 35 Finally, in FIGS. 11, 12 and 13 the two nut screws 38 for controlling the screws 32' have a wire wound up thereon, this wire 39 suitably providing for a connection thereof by passing on idle rollers-40. Upon rotation of a nut screw 38 by means of a knurled .wheel 41 held fast thereto the wire will wind up on one side of the nut screw, while unwinding from the other side and causing the other nut screw to rotate.

As abovementioned, the plate carrying ring 42 can be directly connected to the stationary ring 21 of the craniostat (FIG. 14 and FIG. 1-3), or to. the shoe or sliding block 11 (FIG. 15 in both cases by means of a hinge 43 enabling it to oscillate; in the first case, from a position sidewise of ring 21, said frame or ring 42 and associated plate can be turned over on ring 21, and in the second case, from a position at right angles to the rays to a position parallel thereto(where an intraoral plate is used, the plate holder being therefore unnecessary).

It should be noted that, where the plate holder is restrained to the stationary ring, upon rotation of the cross element through 180, such as to move the X-ray tube unit from left to right, the plate holder frame or ring would be located between said X-ray tube unit and craniostat. Thus, a hinge 43 symmetrical to hinge 43 should be provided on the stationary ring for removing the plate holder frame or ring from said hinge 43 and engaging it on hinge 43.

The device for controlling the earcap alignment (FIG. 16) comprises a hollow tube 101 made of rayopaque material, which is incorporated in the transparent plastics of one of said earcaps, and a full or solid cylinder 102 made of the same material, having a diameter less than the inner diameter of said tube 101, aligned therewith and incorporated in the other earcap. When arranging the craniostat with the earcaps 23 aligned at a side radiography position and projecting on a plate, an image 103 is provided as essentially comprising an opaque ring of a major diameter and an opaque ring of a minor diameter, rings that should be concentric for a good alignment.

From the foregoing it will be apparent that, referring again to FIGS. 1 and 2, the apparatus at its position as shown by full lines in FIG. 1, will enable one to carry out front teleradiographs when the earcaps are perpendicular to the rod; side teleradiographs when the movable ring 22 of the craniostat has been rotated to bring said earcaps parallel to the rod, left and right side radiographs when the craniostat is moved nearer the X-ray tube and the earcaps are at a suitable position; at the position as shown by broken lines in FIG. '1 and obtained by rotating said rod 4 through 90. By inwardly sliding the craniostat and rotating the latter through 90 relative to the previous position, top occlusal radiographs can be performed (in this case the plate holder not being used); at its position as shown in FIG. 2 and obtained by rotating said rod through an angle less than 90 (with respect to the first position), by rotating the craniostat to arrange it at right angles to the rays and turning the plate holder over the craniostat, will enable one to carry out bottom occlusal radiographs. It is also apparent that, as desired, the X-ray tube could be located rightwards or leftwards of the vertical standard.

It is to be understood that all of the modifications and changes in the range of those skilled in the art arewithin the covering field of the invention. For example, the two semirods supporting the X-ray tube and the craniostat, respectively, could be located on the same axis, provided that the earcaps are on the line as defined by the rays from the tube. In this case, for the craniostat rotation, pivoting will be between the bracket and craniostat, rather than between the bracket and rod.

It is also to be understood that the couplings for sliding and rotational motion between the cross rod and standard, or between the craniostat supporting bracket and semirod could have many other technical solutions which have not been described herein, as readily obtainable by any skilled person in mean.

What is claimed is:

1. An apparatus useful for performing cranium and dental radiographs and teleradiographs comprising:

1. a vertical standard;

2. a cross element formed of first and second rods which are fixedly attached to each other, said cross element being both vertically movable along said vertical standard and rotatable with respect to said vertical standard about a first horizontal axis disposed at a right angle to said vertical standard;

3. a source of X-rays carried by said first rod;

a radiographic plate holder and a craniostat carn'ed by said second rod, said craniostat comprising a crown-like upper frame having an internal free area, as viewed from above a patients head in position therein, substantially larger than the projection ofa human head and including adjustable head positioning members extending from said upper frame toward said internal free area for positioning a human head in various positions relative to said X-ray source, said craniostat being longitudinally movable along said second rod and being rotatable about a second horizontal axis disposed at a right angle to said second rod;

5. means for adjusting and fixing said cross element at various longitudinal positions along said vertical standard;

6. means for adjusting and fixing said cross element at various rotational positions about said first horizontal axis;

7. means for adjusting and fixing said craniostat at various longitudinal positions along said second rod; and

8. means for adjusting and fixing said craniostatat various rotational positions about said second horizontal axis.

2. The apparatus as claimed in claim 1 wherein said first and second rods are longitudinally aligned.

3. The apparatus as claimed in claim 1 wherein said upper frame comprises:

a first outer ring carried by a bracket which is connected to said second rod;

a second inner ring concentric with and smaller than said first outer ring and being adjustably rotatable relative thereto about the common axis of the two rings, said second movable ring being carried by said first ring and carrying said adjustable head positioning members; and

means for adjusting said members at various positions around said second ring.

4. The apparatus as claimed in claim 3 wherein the peripheral internal surface of one of said rings is provided with an annular rib of toric cross-section, while the other of said rings is provided with idle concave contour rollers fixedly attached thereto and engaging said rib for movably carrying said other ring relative to said one ring attached to the bracket, while allowing the rotation of said other movable ring with respect to said one ring.

5. The apparatus as claimed in claim 4 wherein a spring projecting means is provided on one of said rings for engaging one of a plurality of notches on the other ring for defining a number of readily available positions between said two rings. i

6. The apparatus as claimed in claim 3 wherein the rotation of said second ring relative to said first ring is provided by a roller coupling, the rollers of which are disposed for sliding within grooves formed by the facing surfaces of substantially horizontal annular extensions of said first and second rings.

7. The apparatus as claimed in laim 3 wherein said head positioning members comprise two symmetric and substantially aligned earpins extending from said second movable ring toward said internal free area, said earpins each being carried by a stem and being movable toward and away from each other wherein the movement of said stems toward and away from each other is symmetrically controlled by a two-lever system moving two pegs connected to said stems, said levers being operated by a single control screwv 8. The apparatus as claimed in claim 3 wherein said head positioning members comprise two symmetric and substantially aligned earpins extending from said second movable ring toward said internal free area,

said earpins each being carried by a stem and being movable toward and away from each other wherein the movement of said stems toward and away from each other is symmetrically controlled respectively by two screws connected to a'wire winding system, wherebyon controlling a first of said two screws by rotating a knob fixedly connected thereto and to a winding bobbin, the second of said two screws also rotates to the same extent as the first screw.

9. The apparatus as claimed in claim 3 wherein said head positioning'members comprise two symmetric and substantially aligned earpins extending from said second movable ring toward said internal free area, said earpins each being carried by a stem and being movable toward and away from each other wherein the movement of said stems toward and away from each other is symmetrically controlled respectively by two screws connected to a crown gear system, whereby on controlling a first of said two screws by a gear wheel fixedly connected thereto, said gear wheel engages said crown gear causing it to rotate, the rotation of the crown gear causing a second gear wheel fixedly connected to the second of said two screws to rotate to the same extent, thereby assuring equal rotation of both of said two screws.

10. The apparatus as claimed in claim 3 wherein the radiographic plate holder is hingedly'connection to said first ring.

11. The apparatus as claimed in claim 3 wherein said bracket is connected to a block which is slidable on said second rod, said radiographic plate holder being hingedly connected to said slidable block.

12. The apparatus as claimed in claim 3 wherein said head positioning members comprise two symmetric and substantially aligned earpins extending from said second movable ring toward said internal free area, said earpins each being carried by a stem and being movable toward and away from each other wherein a means is provided for controlling the earpin alignment,

said means comprising an X-ray-opaque tube in one of said earpins and in the other earpin, an xrray-opaque cylinder of a diameter less than the diameter of said X- ray-opaque tube, whereby the earpins are aligned by aligning said cylinder with said tube by concentrically disposing said cylinder within the larger circle formed by said tube.

13. The apparatus as claimedin claim 1 wherein said means (6) for fixing the rotational movement of said cross element comprises a peg attached to said vertical standard and adapted to engage one of a plurality of holes in a rotatable pin carrying said cross element,

each of said holes corresponding to a predetermined position.

14. The apparatus as claimed in claim 1 wherein said means (7) comprises a block which is slidable along slide gate guides carried by said second rod, said craniostat being carried on said slidable block by a bracket,

and wherein said means (8) comprises a pin on said slidable block carrying said bracket, said pin being rotatable. 1

15. The apparatus as claimed in claim 14 wherein one of said slidable blockor bracket is provided with a spring projecting means on the surface thereof which faces the other of said slidable block or bracket, and wherein the other of said slidable block or bracket is provided with notches for accommodating said projecting'means, so as to define a number of readily available longitudinal and rotational positions for said bracket and craniostat, with respect to said cross element. 

1. An apparatus useful for performing cranium and dental radiographs and teleradiographs comprising:
 1. a vertical standard; 2 a cross element formed of first and second rods which are fixedly attached to each other, said cross element being both vertically movable along said vertical standard and rotatable with respect to said vertical standard about a first horizontal axis disposed at a right angle to said vertical standard; 3 a source of X-rays carried by said first rod; 4 a radiographic plate holder and a craniostat carried by said second rod, said craniostat comprising a crown-like upper frame having an internal free area, as viewed from above a patient''s head in position therein, substantially larger than the projection of a human head and including adjustable head positioning members extending from said upper frame toward said internal free area for positioning a human head in various positions relative to said X-ray source, said craniostat being longitudinally movable along said second rod and being rotatable about a second horizontal axis disposed at a right angle to said second rod; 5 means for adjusting and fixing said cross element at various longitudinal positions along said vertical standard;
 6. means for adjusting and fixing said cross element at various rotational positions about said first horizontal axis;
 7. means for adjusting and fixing said craniostat at various longitudinal positions along said second rod; and 8 means for adjusting and fixing said craniostat at various rotational positions about said second horizontal axis.
 2. The apparatUs as claimed in claim 1 wherein said first and second rods are longitudinally aligned.
 3. The apparatus as claimed in claim 1 wherein said upper frame comprises: a first outer ring carried by a bracket which is connected to said second rod; a second inner ring concentric with and smaller than said first outer ring and being adjustably rotatable relative thereto about the common axis of the two rings, said second movable ring being carried by said first ring and carrying said adjustable head positioning members; and means for adjusting said members at various positions around said second ring.
 4. The apparatus as claimed in claim 3 wherein the peripheral internal surface of one of said rings is provided with an annular rib of toric cross-section, while the other of said rings is provided with idle concave contour rollers fixedly attached thereto and engaging said rib for movably carrying said other ring relative to said one ring attached to the bracket, while allowing the rotation of said other movable ring with respect to said one ring.
 5. The apparatus as claimed in claim 4 wherein a spring projecting means is provided on one of said rings for engaging one of a plurality of notches on the other ring for defining a number of readily available positions between said two rings.
 6. The apparatus as claimed in claim 3 wherein the rotation of said second ring relative to said first ring is provided by a roller coupling, the rollers of which are disposed for sliding within grooves formed by the facing surfaces of substantially horizontal annular extensions of said first and second rings.
 6. means for adjusting and fixing said cross element at various rotational positions about said first horizontal axis;
 7. means for adjusting and fixing said craniostat at various longitudinal positions along said second rod; and 8 means for adjusting and fixing said craniostat at various rotational positions about said second horizontal axis.
 7. The apparatus as claimed in laim 3 wherein said head positioning members comprise two symmetric and substantially aligned earpins extending from said second movable ring toward said internal free area, said earpins each being carried by a stem and being movable toward and away from each other wherein the movement of said stems toward and away from each other is symmetrically controlled by a two-lever system moving two pegs connected to said stems, said levers being operated by a single control screw.
 8. The apparatus as claimed in claim 3 wherein said head positioning members comprise two symmetric and substantially aligned earpins extending from said second movable ring toward said internal free area, said earpins each being carried by a stem and being movable toward and away from each other wherein the movement of said stems toward and away from each other is symmetrically controlled respectively by two screws connected to a wire winding system, whereby on controlling a first of said two screws by rotating a knob fixedly connected thereto and to a winding bobbin, the second of said two screws also rotates to the same extent as the first screw.
 9. The apparatus as claimed in claim 3 wherein said head positioning members comprise two symmetric and substantially aligned earpins extending from said second movable ring toward said internal free area, said earpins each being carried by a stem and being movable toward and away from each other wherein the movement of said stems toward and away from each other is symmetrically controlled respectively by two screws connected to a crown gear system, whereby on controlling a first of said two screws by a gear wheel fixedly connected thereto, said gear wheel engages said crown gear causing it to rotate, the rotation of the crown gear causing a second gear wheel fixedly connected to the second of said two screws to rotate to the same extent, thereby assuring equal rotation of both of said two screws.
 10. The apparatus as claimed in claim 3 wherein the radiographic plate holder is hingedly connection to said first ring.
 11. The apparatus as claimed in claim 3 wherein said bracket is connected to a block which is slidable on said second rod, said radiographic plate holder being hingedly connected to said slidable block.
 12. The apparatus as claimed in claim 3 wherein said head positioning members comprise two symmetric And substantially aligned earpins extending from said second movable ring toward said internal free area, said earpins each being carried by a stem and being movable toward and away from each other wherein a means is provided for controlling the earpin alignment, said means comprising an X-ray-opaque tube in one of said earpins and in the other earpin, an X-ray-opaque cylinder of a diameter less than the diameter of said X-ray-opaque tube, whereby the earpins are aligned by aligning said cylinder with said tube by concentrically disposing said cylinder within the larger circle formed by said tube.
 13. The apparatus as claimed in claim 1 wherein said means (6) for fixing the rotational movement of said cross element comprises a peg attached to said vertical standard and adapted to engage one of a plurality of holes in a rotatable pin carrying said cross element, each of said holes corresponding to a predetermined position.
 14. The apparatus as claimed in claim 1 wherein said means (7) comprises a block which is slidable along slide gate guides carried by said second rod, said craniostat being carried on said slidable block by a bracket, and wherein said means (8) comprises a pin on said slidable block carrying said bracket, said pin being rotatable.
 15. The apparatus as claimed in claim 14 wherein one of said slidable block or bracket is provided with a spring projecting means on the surface thereof which faces the other of said slidable block or bracket, and wherein the other of said slidable block or bracket is provided with notches for accommodating said projecting means, so as to define a number of readily available longitudinal and rotational positions for said bracket and craniostat, with respect to said cross element. 